The present invention relates to a nitride semiconductor substrate to be used as a substrate for a blue light-emitting diode or a blue semiconductor laser device or the like, a method of manufacturing the semiconductor substrate, a semiconductor device employing the nitride semiconductor substrate, and a pattern forming method for the manufacture of the semiconductor device.
Conventionally, semiconductor devices such as a blue light-emitting diode (blue LED) or a blue semiconductor laser device employing a group III nitride such as GaN (gallium nitride), InN (indium nitride), AlN (aluminum nitride), or their mixed crystals, have been in most cases formed on a sapphire substrate.
In the manufacturing process of the semiconductor devices employing the nitride semiconductor, particularly in the manufacturing process of semiconductor laser devices, registration errors on the order of 1 xcexcm do not pose any practical problems. Accordingly, a sufficient registration accuracy can be ensured by using inexpensive exposure apparatus (costing about ten thousand yen per unit) using g-line (wavelength 436 nm) or i-line (wavelength 365 nm) of a mercury lamp, instead of the expensive KrF steppers (costing several billion yen per unit), which are used in the photolithography process for Si (silicon).
However, there was a problem that with an increasing use of a nitride semiconductor substrate as a substrate for the semiconductor device, the accuracy of the resist pattern (hereinafter referred to as a pattern accuracy) drops in the photolithography step during the formation of the semiconductor device, particularly when the pattern is formed by the exposure apparatus using the g- or i-line of the mercury lamp, thereby significantly lowering the yield of the semiconductor device.
Accordingly, it is an object of the invention to improve the pattern accuracy in the photolithography step during the manufacture of the semiconductor device using the nitride semiconductor substrate.
To achieve this object, the present inventors analyzed the cause of deterioration in the pattern accuracy during the pattern formation by the g- or i-line when the conventional nitride semiconductor substrate is used. The analysis revealed the following facts.
FIG. 23 illustrates the exposure of the resist film formed on a conventional nitride semiconductor substrate, specifically a substrate made from GaN (hereinafter referred to as a GaN substrate).
As shown in FIG. 23, a resist film 2 on a GaN substrate 1 is irradiated with an exposure light beam 4 such as the i-line through a photomask 3 with an opening 3a. The wavelength of light that can be absorbed by the nitride semiconductor is short, such as no more than 360 nm in the case of GaN. Accordingly, when the g- or i-line is used as the exposure light beam 4, the exposure light beam 4 that is incident on the surface of the GaN substrate 1 through the resist film 2, i.e., an incident light beam 4, propagates through the GaN substrate 1 without being absorbed. As a result, the incident light beam 4 splits into an emitted light 5 emitted from the back surface of the GaN substrate 1 and a reflected light 6 due to the reflection by the back surface of the GaN substrate 1. When the back surface of the GaN substrate 1 is specular, its reflectance with respect to the incident light beam 4, i.e., the reflectance of the interface between the GaN substrate 1 and air with respect to the incident light beam 4, is as much as about 20%.
A region 2a of the resist film 2 is the region to be exposed by the incident light beam 4. However, as the resist film 2a is exposed from below by the reflected light beam 6, a region 2b of the resist film 2 which is not to be exposed is also exposed. This results in defects such as a peeling of the resist film 2 or a reduction in the resist pattern size, thereby preventing a correct pattern formation in the case of using the conventional nitride semiconductor substrate.
It was also found that the problem of deterioration in the pattern accuracy is pronounced when the intensity of the reflected light beam 6 is increased by a reduction in the thickness of the GaN substrate 1 which makes it easier for the incident light beam 4 to pass through the GaN substrate 1, or when the opening width of the opening 3a of the photomask 3 is not more than several times the wavelength of the incident light beam 4 or exposure light beam, in which case the incident light beam 4, after passing through the opening 3a, is diffracted towards the outside of the opening 3a, with the reflected light beam 6 being extended further outside (see FIG. 23).
It should be noted that in the present specification, the term xe2x80x9creflectionxe2x80x9d means specular reflection (angle of incidence=angle of reflection), and the term xe2x80x9creflectancexe2x80x9d means specular reflectance. Reflections other than the specular reflection are referred to as xe2x80x9cdiffuse reflectionsxe2x80x9d. The term xe2x80x9csubstrate surfacexe2x80x9d refers to the surface on which a nitride semiconductor layer is grown during the manufacture of the semiconductor device using the nitride semiconductor substrate.
Based on the above-mentioned findings, the present invention provides a first semiconductor substrate comprising a semiconductor layer having a group III nitride as a main component, wherein a scattering portion for scattering an incident beam of light entering the semiconductor layer through one plane thereof is provided on another plane or inside of the semiconductor layer.
In the first semiconductor substrate of the invention, the scattering portion for scattering the incident beam of light entering the semiconductor layer from one plane thereof is provided at another plane or inside the semiconductor layer, the semiconductor layer forming the substrate and having a group III nitride as the main component. Accordingly, the intensity of the reflected beam of light created by the reflection of the incident light beam by the another plane can be reduced. This prevents the problem of exposing a region of the resist film that is not to be exposed by the exposure light beam entering through the one plane (hereinafter sometimes referred to as a substrate surface) and reflected by the another surface (hereinafter sometimes referred to as a substrate back surface), in a photolithography step for the manufacture of a semiconductor device using the first semiconductor substrate, i.e., a nitride semiconductor substrate. Thus the pattern accuracy in the photolithography step can be increased and therefore the manufacturing yield of the nitride semiconductor device can be improved. For example, if the first semiconductor substrate is a GaN substrate, particularly the reflection of the g- or i-line of the mercury lamp can be surely prevented, so that the pattern accuracy in the photolithography step using the g- or i-line as the exposure light beam can be significantly improved, with a resultant significant improvement in the manufacturing yield of the nitride semiconductor device.
In the first semiconductor substrate of the invention, the scattering portion preferably may comprise height irregularity formed on the another plane of the semiconductor layer, the height irregularity having a height difference of {fraction (1/10)} or more of the wavelength of the incident beam of light.
This makes the incident beam of light efficiently diffused, i.e., scattered, on the another plane, thereby reducing the reflectance of the another plane against the incident beam of light and thus surely reducing the intensity of the reflected light.
In another embodiment of the invention, the reflectance of the another plane of the semiconductor layer against the incident beam of light is preferably 13% or less, and the wavelength of the incident beam of light is preferably 365 nm (i-line) or 436 nm (g-line).
In yet another embodiment of the invention, the scattering portion is preferably provided inside the semiconductor layer and includes particles or layer of a material having a different index of refraction than that of the group III nitride with respect to the incident beam of light.
In this embodiment, since the incident beam of light can be efficiently scattered inside the semiconductor layer, the intensity of the reflected beam of light can surely be reduced.
The diameter of each particle of the material, the width of the layer of the material in a direction parallel to the one plane, or the thickness of the layer of the material, are in each case about {fraction (1/10)} or more of the wave length of the incident beam of light. It is also preferable that the particles or layer of the material are provided in a direction parallel to the one plane of the semiconductor layer, that the scattering portion is provided in a direction parallel to the one plane of the semiconductor layer, and that the scattering portion includes another semiconductor layer having the group III nitride as a main component and the particles or layer stacked alternately. The scattering portion preferably has a thickness of about {fraction (1/10)} or more of the wave of the incident beam of light. The above-mentioned material is preferably Si, SiO2, SiN or Al2O3. The scattering portion preferably has a transmittance of 80% or less with respect to the incident beam of light, and the wave of the incident beam of light is preferably 365 nm or 436 nm.
A second semiconductor substrate according to the present invention comprises a semiconductor layer having a group III nitride as a main component, wherein a transmitting portion for transmitting an incident beam of light entering the semiconductor layer from one plane thereof is provided on another plane of the semiconductor layer.
In accordance with the second semiconductor substrate, the transmitting portion for transmitting the incident beam of light entering the semiconductor layer forming the substrate from the one plane thereof is provided on the another plane of the semiconductor layer, the semiconductor layer having a group III nitride as a main component. Accordingly, the reflectance of the another plane with respect to the incident beam of light can be reduced, whereby the intensity of the reflected light caused by the reflection of the incident beam of light by the another plane. Thus, the problem of exposing a region of the resist film that is not to be exposed by the exposing beam of light entering from the one plane (substrate surface) and reflected by the another plane (substrate back surface) can be prevented in the photolithography step in the manufacture of a semiconductor device using the second semiconductor substrate or nitride semiconductor substrate. The pattern accuracy in the photolithography step can therefore be improved and thus the manufacturing yield of the nitride semiconductor device can be increased. For example, when the second semiconductor substrate is a GaN substrate, particularly the reflection of the g- or i-line of the mercury lamp by the substrate back surface can be surely prevented. As a result, the pattern accuracy in the photolithography step using the g- or i-line as the exposing beam of light can be significantly improved, resulting in a significantly improved manufacturing yield of the nitride semiconductor device.
In the second semiconductor substrate, the transmitting portion preferably comprises a layer formed on the another plane of the semiconductor layer, the layer formed from a material with a different index of refraction than that of the group III nitride with respect to the incident beam of light.
In this manner, the reflectance of the another plane with respect to the incident beam of light can be surely reduced.
In this case, the layer of the above-mentioned material preferably is composed of a plurality of layers, of which at least two have different indexes of refraction with respect to the incident beam of light. The material preferably has an index of refraction which is about {fraction (9/10)} or less of that of the group III nitride with respect to the incident beam of light. The material is preferably SiO2, SiN or Al2O3, a compound of the group III element forming the semiconductor layer and oxygen, or AlxGa1xe2x88x92xN (0 less than xxe2x89xa61). In the case where the material is a compound of the group III element forming the semiconductor layer and oxygen, the manufacturing process can be simplified as compared with the case of forming a transmitting portion newly on the substrate back surface in the form of a film. Further, the potential mixture of an impurity into the substrate can be prevented, thereby improving the manufacturing yield of the substrate.
In the second semiconductor substrate, the transmitting portion preferably has a transmittance of 80% or more with respect to the incident beam of light.
By doing so, the reflectance of the another plane against the incident light can be surely reduced. Further, it is also preferable that the wavelength of the incident light is 365 nm or 436 nm.
In the second semiconductor substrate, it is further preferable that a scattering portion is provided either between the another plane of the semiconductor layer and the transmitting portion or inside the semiconductor layer for scattering the incident light.
By so doing, the incident light is first scattered by the scattering portion and then transmitted by the transmitting portion, so that the intensity of the reflected light can be further reduced.
A third semiconductor substrate according to the invention comprises a semiconductor layer having a group III nitride as a main component, wherein an absorbing portion for absorbing the incident beam of light entering the semiconductor layer from one plane thereof is provided at least a part of the semiconductor layer.
In the third semiconductor substrate, the absorbing portion for absorbing the incident beam of light entering from the one plane of the semiconductor layer, which forms the substrate and has the group III nitride as a main component, is provided at least a part of the semiconductor layer. Accordingly, the intensity of the reflected beam of light caused by the reflection of the incident beam of light on the another plane can be reduced. Thus, in the photolithography step for the manufacture of a semiconductor device using the third semiconductor substrate or nitride semiconductor substrate, the problem of exposing a region of the resist film that is not to be exposed by the exposing beam of light entering from the one plane (substrate surface) and reflected by the another plane (substrate back surface) can be avoided. As a result, the pattern accuracy in the photolithography step can be improved, and therefore the manufacturing yield of the nitride semiconductor device can be improved. For example, when the third semiconductor substrate is a GaN substrate, particularly the reflection o the g- or i-line of the mercury lamp by the substrate back surface can be surely prevented, so that the pattern accuracy in the photolithography step using the g- or i-line as the exposing beam of light can be significantly increased, thereby also improving the manufacturing yield of the nitride semiconductor device.
In the third semiconductor substrate, it is preferable that the transmittance of the absorbing portion against the incident beam of light is 80% or less.
By so doing, even when the substrate back surface is specular, the reflectance of the substrate back surface against the incident beam of light can be reduced to substantially 13% or lower, thereby surely improving the pattern accuracy in the photolithography step. Also, the wavelength of the incident beam of light is preferably 365 nm or 436 nm.
In the third semiconductor substrate, the absorbing portion is preferable made from a material with a larger absorption coefficient than that of the group III nitride with respect to the incident beam of light.
By so doing, the incident beam of light can be surely absorbed by the absorbing portion, whereby the intensity of the incident beam of light can be surely reduced. In this case, it is preferable that the material is composed of a plurality of materials having different absorption coefficients with respect to the incident beam of light, or includes at least one of Si and W.
In the third semiconductor substrate, the absorption portion is formed by adding an impurity to the semiconductor layer such that a level arises that absorbs the incident beam of light.
By so doing, the incident beam of light can be surely absorbed by the absorbing portion, so that the intensity of the reflected beam of light can be surely reduced, and the lowering of crystallinity of the third semiconductor substrate or nitride semiconductor substrate can be prevented. Further, the impurity preferably contains at least one of C, O, Si, S, Cl, P and As. It is also preferable that the relationship z0 0.223/xcex1 holds where xcex1 is the absorption coefficient of the absorbing portion with respect to the incident beam of light and z0 is the thickness of the absorbing portion.
In the third semiconductor substrate, the absorbing portion preferably comprises point defects formed in the semiconductor layer.
By so doing, the incident beam of light can be surely absorbed by the absorbing portion, so that the intensity of the reflected beam of light can be surely reduced, and also the lowering of crystallinity of the third semiconductor substrate or nitride semiconductor substrate can be prevented. In this case, the point defects are preferably formed by introducing protons into the semiconductor layer.
In the third semiconductor substrate, the absorbing portion is preferably distributed non-uniformly along a direction parallel to the one plane of the semiconductor layer.
By so doing, not only does the absorbing portion absorbs the incident beam of light but also it scatters the incident beam of light, so that the intensity of the reflected beam of light can be further reduced. Further, when producing a ridge-type laser device by using the semiconductor substrate, by not providing the absorbing portion on the lower side of the ridge structure in the semiconductor substrate, the pattern accuracy in the photolithography step can be improved without adversely affecting the characteristics of the activation layer of the substrate.
A first method of manufacturing a semiconductor substrate according to the present invention includes the steps of: partially forming a light scattering portion on a first semiconductor layer having a group III nitride as a main component, the light scattering portion formed from a material with different optical index of refraction than that of the group III nitride; and crystal-growing a second semiconductor layer having the group III nitride as a main component on the first semiconductor layer including the light scattering portion, whereby a semiconductor substrate comprising the first semiconductor layer, the light scattering portion and the second semiconductor layer is formed.
In accordance with the first method of manufacturing the semiconductor substrate, since the light scattering portion is formed between the first semiconductor layer and the second semiconductor layer forming the semiconductor substrate, the intensity of the light entering from the substrate surface and then reflected by the substrate back surface, i.e., a reflected beam of light can be reduced. Accordingly, in the photolithography step for the manufacture of a nitride semiconductor device using this semiconductor substrate, the problem of exposing a region of the resist film that is not to be exposed can be avoided, thereby increasing the pattern accuracy and increasing the manufacturing yield of the nitride semiconductor device.
Further, in accordance with the first method of manufacturing the semiconductor substrate, after partially forming the light scattering portion from a material with different index of refraction than that of the first semiconductor layer, i.e. from a different material than that of the first semiconductor layer, the second semiconductor layer is crystal-grown on the first semiconductor layer including the light scattering portion. This makes it possible to prevent the defects and the like present in the first semiconductor layer from being conveyed to the second semiconductor layer. Thus, an excellent crystallinity of the second semiconductor layer can be ensured, thereby also ensuring the excellent crystallinity of the semiconductor substrate having the light scattering portion.
In the first method of manufacturing the semiconductor substrate, the step of partially forming the light scattering portion preferably comprises the step of forming a film on the entire surface of the semiconductor layer to serve as the optical scattering portion, the step of partially forming a mask pattern on the film, etching the film by means of the mask pattern and removing the portions of the film that were not covered by the mask pattern, thereby forming the light scattering portion, and the step of removing the mask pattern.
In this way, the light scattering portion can be reliably formed partially on the first semiconductor layer.
A second method of manufacturing the semiconductor substrate according to the invention comprises the steps of: forming height irregularity on the back surface of a semiconductor layer having a group III nitride as a main component, the height irregularity having a height difference larger than a predetermined value; and forming an imbedded film on the back surface of the semiconductor layer with the height irregularity formed, the imbedded film formed from a material with a different optical index of refraction than that of the group III nitride, whereby a semiconductor substrate comprising the semiconductor layer and the imbedded film is formed.
In accordance with the second method of manufacturing the semiconductor substrate, the height irregularity forming the light scattering potion are formed on the back surface of the semiconductor layer forming the semiconductor substrate, i.e., on the interface between the semiconductor layer and the imbedded film. This makes it possible to reduce the intensity of the light entering from the substrate surface and then reflected by the substrate back surface, i.e., the reflected beam of light. Accordingly, in the photolithography step for the manufacture of the nitride semiconductor device using the semiconductor substrate, the problem of exposing the regions of the resist film that are not to be exposed can be avoided, so that the pattern accuracy can be increased and the manufacturing yield of the nitride semiconductor device can be improved.
Further, in accordance with the second method of manufacturing the semiconductor substrate, since the back surface of the semiconductor layer which was made coarse by the height irregularity can be flattened by the imbedded film, the substrate back surface can be flattened and the manufacturing process of the semiconductor device can be simplified.
Further, in accordance with the second method of manufacturing the semiconductor substrate, when another semiconductor layer having the group III nitride as a main component is crystal-grown as the embedded film, an excellent crystallinity can be obtained in the another semiconductor layer formed on the convex portions of the height irregularity. Accordingly, an excellent crystallinity can be obtained in the semiconductor substrate having the light scattering portion.
A third method of manufacturing the semiconductor substrate according to the invention comprises the steps of: partially forming a light absorbing portion on the first semiconductor layer having the group III nitride as the main component, the light absorbing portion formed from a material with a larger optical absorption coefficient than that of the group III nitride; crystal-growing a second semiconductor layer on the first semiconductor layer including the light absorbing portion, the second semiconductor layer having the group III nitride as the main component, whereby a semiconductor substrate comprising the first semiconductor layer, the light absorbing portion and the second semiconductor layer is formed.
In accordance with the third method of manufacturing the semiconductor substrate, the light absorbing portion is formed between the first semiconductor layer forming the semiconductor substrate and the second semiconductor layer. Accordingly, the light entering from the substrate surface and then reflected by the substrate back surface, i.e., a reflected beam of light can be reduced in intensity. Thus, in the photolithography step for the manufacture of the nitride semiconductor device using this semiconductor substrate, the problem of exposing the regions of the resist film that are not to be exposed can be prevented, whereby the pattern accuracy can be improved and the manufacturing yield of the nitride semiconductor device can be increased.
Further, in accordance with the third method of manufacturing the semiconductor substrate, after partially forming the light absorbing portion from a material with different absorption coefficient than that of the first semiconductor layer, i.e. from a different material than that of the first semiconductor layer, the second semiconductor layer is crystal-grown on the first semiconductor layer including the light absorbing portion. Accordingly, the conveyance of the defects and the like present in the first semiconductor layer to the second semiconductor layer can be prevented by the light absorbing portion. Thus, an excellent crystallinity can be obtained in the semiconductor substrate having the light absorbing portion.
A fourth method of manufacturing the semiconductor substrate in accordance with the invention comprises the step of forming the light absorbing portion by implanting an impurity into the semiconductor layer having the group III nitride as the main component, thereby establishing a level that absorbs light, whereby a semiconductor substrate comprising the semiconductor layer and the light absorbing portion is formed.
In accordance with the fourth method of manufacturing the semiconductor substrate, the light absorbing portion is formed in the semiconductor layer forming the semiconductor substrate, so that the light entering from the substrate surface and then reflected by the substrate back surface, i.e. a reflected beam of light, can be reduced in intensity. This makes it possible to prevent the problem of exposing the regions of the resist film that are not to be exposed in the photolithography step for the manufacture of the nitride semiconductor device using this semiconductor substrate. Accordingly, the pattern accuracy can be increased and therefore the manufacturing yield of the nitride semiconductor device can be improved.
Further, in accordance with the fourth method of manufacturing the semiconductor substrate, since the light absorbing portion is formed by implanting an impurity into the semiconductor layer forming the substrate, the lowering of the crystallinity of the semiconductor substrate having the light absorbing portion can be prevented.
In accordance with the fourth method of manufacturing the semiconductor substrate, the step of forming the light absorbing portion preferably comprises the step of partially forming the light absorbing portion in the semiconductor layer by partially forming a mask pattern on the semiconductor layer and then implanting an impurity into the semiconductor layer with the use of the mask pattern, and the step of removing the mask pattern.
In this manner, the light absorbing portion can be surely formed partially on the semiconductor layer. When a ridge-type laser device is produced using the semiconductor substrate, for example, the pattern accuracy in the photolithography step can be improved without adversely affecting the characteristics of the activation layer on the semiconductor substrate by not providing the absorbing portion on the lower side of the ridge structure of the semiconductor substrate.
A first semiconductor device according to the invention comprises a semiconductor substrate having a group III nitride as a main component and a scattering portion for scattering light entering from one plane of the substrate, the scattering portion provided on another plane or inside of the substrate, and a structure formed on the one plane of the semiconductor substrate by a photolithography and etching of the semiconductor layer of the group III nitride.
In accordance with the first semiconductor device, which employs the first semiconductor substrate according to the invention, no undesired exposure of the resist film occurs during the photolithography step. As a result, the dimensional accuracy of the structure formed on the substrate can be improved and therefore the manufacturing yield of the semiconductor device can be improved.
A second semiconductor device according to the invention comprises a semiconductor substrate having a transmitting portion for transmitting light entering from one plane of the substrate and having a group III nitride as a main component, the transmitting portion provided on another plane of the substrate, and a structure formed on the one plane of the semiconductor substrate by a photolithography and etching of the semiconductor layer of the group III nitride.
In accordance with the second semiconductor device, which employs the second semiconductor substrate according to the invention, no unwanted exposure of the resist film occurs during the photolithography step. Accordingly, the dimensional accuracy of the structure formed on the substrate can be improved and the manufacturing yield of the semiconductor device can be improved.
A third semiconductor device according to the invention comprises a semiconductor substrate having an absorbing portion for absorbing light entering from one plane of the substrate and having a group III nitride as a main component, the absorbing portion provided at least a part of the semiconductor substrate, and a structure formed on the one plane of the semiconductor substrate by a photolithography and etching of the semiconductor layer of the group III nitride.
In accordance with the third semiconductor device, which employs the third semiconductor substrate according to the invention, no undesired exposure of the resist film occurs during the photolithography step. Accordingly, the dimensional accuracy of the structure formed on the substrate can be improved and therefore the manufacturing yield of the semiconductor device can be improved.
In any of the first to the third semiconductor device, the structure may include a ridge structure or a trench structure.
In the third semiconductor device, the structure comprises a ridge structure, and it is preferable that the absorbing portion is not provided at the lower side of the ridge structure of the semiconductor substrate. In this manner, the pattern accuracy of the photolithography step can be improved without adversely affecting the characteristics of the activation layer on the substrate.
A first pattern forming method according to the invention comprises the steps of: forming a semiconductor layer of a group III nitride on one plane of a semiconductor substrate having a scattering portion for scattering light entering from the one plane of the substrate and having the group III nitride as a main component, the semiconductor substrate, the scattering portion provided on another plane or inside of the semiconductor substrate; forming a positive- or negative-type resist film on the semiconductor layer; irradiating the resist film with a exposing beam of light via a photomask having an opening; forming a resist pattern by developing the resist film so that, where the resist film is of the positive type, portions of the resist film that were irradiated by the exposing beam of light are removed and where the resist film is of the negative type, portions of the resist film that were not irradiated by the beam of exposing beam of light are removed; and etching the semiconductor layer by using the resist pattern as a mask.
In accordance with the first pattern forming method, which is a pattern forming method for the manufacture of the semiconductor device using the first semiconductor substrate according to the invention, the problem of exposing the regions of the resist film that are not to be exposed can be prevented. Accordingly, the resist pattern accuracy can be improved and therefore the manufacturing yield of the semiconductor device can be improved.
A second pattern forming method according to the invention comprises the steps of: forming a semiconductor layer of a group III nitride on one plane of a semiconductor substrate having a transmitting portion provided on another plane of the semiconductor substrate for transmitting a beam of light incident from the one plane, the semiconductor substrate comprising the group III nitride as a main component; forming a positive- or negative-type resist film on the semiconductor layer; irradiating the resist film with an exposing beam of light through a photomask having an opening portion; developing the resist film so that, where the resist film is of positive type, portions of the resist film that were irradiated with the exposing beam of light are removed and where the resist film is of negative type, portions of the resist film that were not irradiated with the exposing beam of light are removed, whereby a resist pattern is formed; and etching the semiconductor layer while using the resist pattern as a mask.
In accordance with the second pattern forming method, which is a pattern forming method for manufacturing the semiconductor device using the second semiconductor substrate according to the invention, the problem of exposing the regions of the resist film that are not to be exposed can be prevented. Accordingly, the resist pattern accuracy can be improved and therefore the manufacturing yield of the semiconductor device can be improved.
A third pattern forming method according to the invention comprises the steps of: forming a semiconductor layer of a group III nitride on one plane of a semiconductor substrate provided at least partially with an absorbing portion for absorbing a beam of light incident from the one plane, the semiconductor substrate comprising the group III nitride as a main component; forming a positive- or negative-type resist film on the semiconductor layer; irradiating the resist film with an exposing beam of light through a photomask having an opening; developing the resist film so that, where the resist film is of positive type, portions of the resist film that were irradiated by the exposing light beam are removed and where the resist film is of negative type, portions of the resist film that were not irradiated by the exposing beam of light are removed, whereby a resist pattern is formed; and etching the semiconductor layer while using the resist pattern as a mask.
In accordance with the third pattern forming method, which is a pattern forming method for the manufacture of the semiconductor device using the third semiconductor substrate according to the invention, the problem of exposing the regions of the resist film that are not to be exposed can be prevented. Accordingly, the resist pattern accuracy can be improved and therefore the manufacturing yield of the semiconductor device can be improved.